5.2.24 Inserting a string before the cursor

Procedure: insstrwin str #:key y x n

This routine inserts a character string (as many characters as will
fit on the line) before the character under the cursor. All characters
to the right of the cursor are shifted right with the possibility of
the rightmost characters on the line being lost. The cursor position
does not change (after moving to y, x, if specified). If
n is specified, it inserts a leading substring of at most n
characters, or if n<=0, then the entire string is inserted.